Use of multiple incremental (through the wall) or window-mounted air conditioning units in hotels, motels and offices is quite common. Typically, such units are regulated by a conventional thermostatic control which activates the compressor whenever the room temperature exceeds the desired room temperature as selected by the occupant and dialed into the thermostat.
Such units are extremely energy inefficient for several reasons. For one, the compressor remains activated as long as the room temperature exceeds the thermostat setting, regardless of how cold the room actually is. Also, as long as the room temperature is higher than the thermostat set temperature, the compressor is continuously activated irrespective of how close the room temperature and thermostat set temperatures are. Since the compressor is by far the largest energy consuming component of such units, these aspects of operation, which result in unnecessary use of the compressor, lead to wasted energy. To reduce some of this waste, it has been suggested to continuously cycle the compressor according to a fixed duty cycle. When this is done, a separate circuit for preventing the compressor from short cycling is generally included, as such short cycling can result in compressor motor failure. While such systems represent an improvement over conventional thermostatically regulated air conditioning units, they still have a number of drawbacks. For one, they do not compensate for the situation where the thermostat setting calls for an extremely low room temperature. This is a common situation in motels, hotels and offices where occupants set the thermostat extremely low upon leaving the room so that the room will be cool when they return. Such systems also fail to compensate for situations where the room tempreature is quite high and it is desirable to have the compressor running continuously rather than cycling.